Optical centering gauge



June 12, 1951 R. s. GRIFFIN OPTICAL CENTERING GAUGE Original Filed Jan.16, 1942 3 Sheets-Sheet 1 Foe THE HEM irroe/vems June 12', 1951 R. s.GRIFFIN 2,557,029

' OPTICAL CENTERING GAUGE Original Filed-Jan. 16, 1942 3 Sheets-Sheet 2F v W? I 120- l l I A INvE/v TOE Fla/4420 57'ANLEY k/Fn/v June 12, 1951R 2,557,029

OPTICAL CENTERING GAUGE Original Filed Jan. 16, 1942 s sheets sheet aINVENTO? T Hex-men 5727NLEY 'e/r -wv v Patented June 12 1951 OPTICALCENTERING GAUGE Richard Stanley Griflin, Glendale, Calif.

Continuation of applicationv Serial No. 427,002, January 16, 1942. Thisapplication March 24, 1945, Serial No. 584,573

8 Claims.

This application is a continuation of my copending application, SerialNo. 427,002, filed January 16, 1942, entitled Method and Means for GageOperations in Machine Work and the Like, and now abandoned.

My invention relates to means pertaining to gages for machine work andsimilar purposes and is directed to an improved precision instrument ofthe optical type. The instrument may be employed for such operations ascentering, truing, laying out, inspecting, testing, and measuring inmachine shop practice and in other fields as well.

The general object of my invention is to provide a reliable gage thatmay be manipulated by an operator of only ordinary skill to produceexceedi'ngly accurate results with great saving in time. It has beendemonstrated that the invention may be practiced by an operator for thefirst time to achieve accuracy within .0001 plus or minus and that aftera little experience the habitual accuracy of a careful operator may beWithin a tolerance of 00005".

A machine tool, such as a lathe, drill press, boring machine, and thelike, has two holding means, one for a tool and the other for a workpiece, one of the holding means rotating relative to the other about anoperation axis. If one of the two holding means, usually the rotaryholding means, is not aligned accurately, the cutting tool operates in acircular orbit about the operating axis relative to the work piece. Thisaberration is commonly termed. run-out. An important object of certainpractices of my invention is to locate the true center or operation axisregardless of whatever run-out may be inherent in a machine.

In one of these practices it is an object of my invention to provide anoptical gage adapted to be mounted on a rotary tool holder for useduring rotation of the tool holder to ascertain the true center oroperation axis regardless of runout. In this particular practice I havethe novel object of providing an optical procedure that makes visible tothe operator a circular orbit representing the run-out, the center ofthe circular orbit being the true center or the point at which theoperation axis intersects the work piece.

In another practice of my invention for locating a true centerregardless of run-out, it is my object to provide an optical gage thatmay be mounted either in a rotary holder or in a stationary holder forlocating the true center while the machine is inactive. A further objecthereis to provide means for locating the true center without thenecessity of ascertaining either the magnitude or the orientation of theinherent divergence that produces the run-out. A further object in thisaspect of my invention is to pro-- vide a correcting means which may beemployed to automatically resolve the unknown divergence into twocomponents which are compensated in succession to locate the truecenter, there being no necessity for ascertaining the actual degree ofthe inherent divergence angle or the instant direction of thedivergence.

A group of objects relating to the optical aspect of the inventionincludes the following: to provide an optical system whereby a line ofsight at least approximately corresponding to the axis of a holdingmeans may be observed longitudinally from a lateral point, i. e., toprovide for a longitudinal line of sight that is bent to a lateralobservation point to afford the observer the equivalent of sighting in astraight line down the axis of the holding means; to provide an accurateline of sight with an adequate field of vision; to provide a visualreference for indicating the location of the line of sight in the fieldof vision; to provide such a visual reference in the form of an imagefor observation with relation to a reference mark on a work piece in thefield of vision; to providesuch a visual reference for identifying theline of' sight that is especially adapted for use with a specialreference mark on a work piece; and to provide an optical system thatinherently avoids any inaccuracy arising from apparent travel of theimage of a mark on a work piece with change in location of the observerseye at the eyepiece of the optical system. My object in one practice ofthe invention is to provide a line of sight in an optical system thatmay be varied for the purpose of performing a centering'procedureregardless of run-out, and a further object is to. provide a simple,reliable and easily adjustable means for causing such variation in theline of. sight.

With reference to. the physical structure of a gage of the present type,one of my important objects is to solve certainexceedingly di-fiicultproblems in precision manufacture, my solution being characterized bythe concept of a construction that comprises largely parts manufactured.to. only ordinary tolerance but adapted for exceedingly preciseadjustment in the course of assembly and. adapted to maintain such.adjustment permanently after assembly. A further object is to provide astandard or basic construction for. the instrument that may be convertedto. various forms of the invention, which forms include what I term avariable center 3 scope, a rotating center scope, and a surface scope.These various forms will be described below.

The above and other objects and advantages of my invention will beapparent in the following detailed description taken with theaccompanying drawings.

In the drawings, which are to be regarded as illustrative only,

Fig. 1 is a longitudinal sectional View of the form of my invention thatI term the rotating center scope;

Fig. 2 is a transverse section taken on the line 22 of Fig. 1;

Fig. 3 is a similar section taken on the line 33 of Fig. 1;

Fig. l is a diagrammatic representation of the field of vision observedin the use of the instrument of Fig. 1;

Fig. 5 is a longitudinal sectional View of the form of the inventionthat I term the variable center scope;

Fig. 6 is a transverse section taken as indicated by the line 6-6 ofFig. 5;

Fig. 7 is a similar section taken as indicated by the line 1-1 of Fi 5;

Fig. 8 is a side elevation on a reduced scale of the instrument of Fig.5 mounted in a drill press;

Fig. 9 is a fragmentary view similar to Fig. 8 on an enlarged scale,showing one of my instruments with an extended optical objective for usewith work pieces presenting certain difficulties;

Figs. 10 to 14 are diagrammatic views of a field of vision illustratingsteps in a centering procedure performed with the variable center scope;

Figs. 15 to 23 are diagrams to further illustrate the spacerelationships involved in the series of steps;

Fig. 24 is a perspective view on a reduced scale of the variable centerscope as set up for centering work in a lathe;

Fig. 25 is a side elevation of the form of my invention that I term thesurface scope; and

Fig. 26 is an end view of the same instrument taken as indicated by thearrow 26 of Fig. 25.

It is to be understood that, while the following description is directedspecifically to instruments for machine shop practice, the principles ofthe invention are widely applicable to diverse purposes in variousfields. The present disclosure will provide adequate guidance to thoseskilled in the art desiring to apply the invention wherever it may haveutility.

The optical gage shown in Figs. 1 to 3 has a housing, generallydesignated 30, that includes a body portion 31 of cylindricalconfiguration and includes integral therewith a cylindrical portion 32which may be termed the eyepiece of the instrument. The housing 36 isrotatably mounted on a coaxial stem or shank 33, whereby the instrumentmay be mounted in a chuck or the like. Inside the housing is a suitableoptical system, to be described later, the optical system including alight-deflecting means, generally designated 35, and providing for aline of sight having a first leg, indicated by the dotted line 36,substantially coaxial with the housing body 3| and a second leg,indicated by the dotted line 31, the second leg being preferablysubstantially coaxial with the cylindrical eyepiece 32. The instrumentis further adapted to provide some visual reference means to indicatethe location of the described line of sight. Preferably '4 I in thepresent device means is incorporated in the optical system to form onthe field of vision an image (Fig. 4) comprising a first pair ofparallel spaced lines 33 and a second pair of parallel spaced lines 40perpendicular thereto, the four lines defining a small square 4|centrally of the field of vision. The line of sight is precisely at thecenter of the square 4|.

It is apparent that the essential elements just described may beembodied in various forms and arrangements. In the particularconstruction indicated in Fig. 1, the housing 36 is rotatably mounted onthe stem 33 by an upper ball bearing comprising an outer race 42 incooperation with an inner race 43, and a lower ball bearing comprisingan outer race cooperating with an inner race 46. The two bearings are inthe form of thrust bearings, and to preclude any play in the bearingsthey may be amply preloaded.

In the present arrangement a cap 41 is threaded onto the upper end ofthe housing body 3l to exert considerable inward pressure on the outerrace 42, the outer race 42 pressing in turn against a spacer sleeve 48that in turn crowds the outer race 45 against an annular shoulder 56 ofthe housing 30. It is contemplated that the spacer sleeve 48 will bemade of metal sufficiently soft to yield in response to compressionincidental to the screwing down of the cap 41. For preloading the innerraces 43 and 46, I employ a suitable helical spring 51 in compressionbetween the two races, the spring tending to compress the ball elementsbetween the inner and outer race. As indicated in Fig. 1, the inner endof the stem 33 may be provided with a suitable retaining nut 52, and thestem may be surrounded by a suitable gasket 53 to serve as a dust sealat the cap 41. When the bearings are initially assembled on the stem 33,the spring 51 presses the inner race 46 against the retaining nut 52 andpresses the inner race 46 against an annular shoulder 55 on theperiphery of the stem, but, when the ca 41 is screwed down, the twoinner races are forced toward each other.

snugly journaled inside the housing body 3| below the two bearings andresting on an annular shoulder 56 of the housing is a block 51 ofcylindrical configuration, having the function of supporting thepreviously mentioned light deflecting means 35, the block being cutaway, as indicated in Fig. 1, to provide light-transmittingcommunication along the previously mentioned line of sight. At the upperend of the block 51 is a semi-cylindrical portion 58 presenting adiametrical face 60 for cooperation with a pair of set screws 61 to.adjustably fix the rotational position of the block. As best shown inFig. 2, these two set screws are threaded into corresponding bores 62 inthe wall of the housing body 3|.

The light-deflecting means 35 may be either light-reflecting orlight-refracting in various practices of the invention. I prefer thepresent arrangement in which the light-deflecting means 35 is a metalbody having a highly polished mirror surface 53, the mirror body beingadjustably mounted on the cylindrical block 51 for rotation about atransverse axis. As indicated in Figs. 1 and 3, the mirror body 35 maybe formed with a pair of cars 65 providing pivot sockets 66 having acommon axis in the plane of the mirror surface 63, the common axis lyingsubstantially at the intersection or juncture of the axis correspondingto the dotted line 36 and the axis corresponding to the dotted line 31.As best shown in Fig. 3, two pointed set screws 6.? mounted in suitablediametric bores 68 in the block 51 enter the two sockets 66 to supportthe mirror body for rotation about the described transverse axis.

For controlling the tilt of the mirror body 35 about the transverse axisof the two set screws 67, I thread an upper set screw I into an upperbore II in the block 57 and thread a lower set screw I2 into a lowerbore I3 in the block, the two set screws impinging against the backsurface of the mirror body 35 on opposite sides of the transverse axis.For access to the two set screws and I2, I provide correspondingrelatively large bores I4 and F5 in the wall of the housing body 3!, thetwo housing bores being oversize to permit the two set screws it and T2to be accessible over an ample range of rotation of adjustment on theart of the block 5?.

The outstanding advantage of the described method of mounting the mirrorbody 33 is that the various elements involved may be initially assembledin only approximately correct positions and then may be conveniently andquickly adjusted to an exceedingly high degree of precision. Thus, afterinitial assembly, the device may be mounted in a suitable jig providingan accurately located target for observation through the eyepiece 32.While the initially assembled instrument is in the jig, the mirror body35 is rotatably adjusted about the axis of the housing body 3| by meansof the two set screws 6i acting on the diametric face 60 of the block 5?and is rotatably adjusted with respect to tilt about the transverse axisby the two set screws I3 and "i2.

After complete adjustment is accomplished by sighting on a target, itwould be found that the mirror surface 53 is rotated to a planeperpendicular to the plane defined by the two dotted lines 36 and 3'?and is tilted to a position making equal angles with the two dottedlines. It has been found in practice that the described elements may beso designed that the transverse axis on which the mirror body 35 ispivoted may lie a substantial distance out of the plane of the mirrorsurface 63, since it is the final position of the mirror surface, ratherthan the axis about which the mirror is adjusted to reach the finalposition, that is important in the actual use of the device.

After precision assembly is accomplished with the various set screwstight to maintain precision, 2. name plate may be employed to concealbores in the housing body 3| and preclude access to the set screws.Figs. 1 to 3 show a name plate 16 retained by headed pins I1, the headedpins being driven into threaded bushings 1-8 in the two bores 32 and inthe bore I5.

A suitable optical system for service in the construction described tothis point may be provided as follows. The outer end of the eyepiece 32is equipped with a suitable cylindrical liner [9, the

liner being telescoped into the eyepiece with a forced fit. At the outerend of the liner I9 in confinement between a suitable bushing 80 and aspacing sleeve BI is an outer lens 82. This outer lens 82 is a doubleconvex lens having a focal length of 1.003", an outside diameter of.685", and

a thickness through the axial center of .187". Theinner end of thespacing sleeve 8 I lies substantially in the focal plane of the lens 82and abuts a flat reticle 83. The reticle 83 is provided on its uppersurface with suitable cross-hairs to formthe previously mentionedpattern of intersecting lines 38 and 40 in the field of vision shown inFig. 4. Underlying the recticle 83 is a stop or aperture plate 85 havingan inner diameter of Th", the stop being supported by a second spacersleeve, 8.6. Confined between the lower end of the spacer sleeve 36v andan inner annular shoulder 8.1 in the liner I9 is a plano convex lenshaving afocal length of 1.997", a diameter of .685", and a thickness of,.120."

Tocomplete the optical system, a tubular obj ective 93. having a radialflange 3| is frictionally telescoped into. the lower end of the housingbody 31. The tubular objective retains a doublet combination of twoplano convex lenses having a focal length of .625", the spacing of thetwo lensesopticalcenter to optical centerbeing .295". In the. particularconstruction shown, a bushing 93 presses the upper of these two lenses92 against a spacer sleeve 95, and the spacer sleeve in turn presses thelower lens against an annular shoulder 96 formed in the tubularobjective.

Fig. 8. illustrates. by way of example how the described optical gagemay be employed for properly positioning a work piece, generallydesignated I 30, on a drill press, the drill press having a tool holdingmeans. in the form of a chuck. I0! on a vertical spindle I02.Preparatory to the centering procedure, the desired location isindicated on the work piece by two lines intersecting each otherperpendicularly. The two dotted lines I 03 in Fig. 4 represent suchreference marks on the work piece as an image in the field of, visionprovided by the above described optical system.

With the work piece H10 in approximately the desired position, theoperator places the optical gage in the chuck IUI, as shown in Fig. 8,and lowers the chuck to bring the optical. gage into focus with thesurface of the work piece. If the intersecting reference lines are notapparent, the work piece is shifted as necessary to bring them into thefield of vision, but the operator need not place the reference marks ina position symmetrical with respect to the reference lines 38 and 40 ofthe optical system. Since the stem or shank 33 of the instrument iscoaxial with the housing body 3! and with the first leg 36 of the lineof sight, the small square 4I formed by the cross-hairs is symmetricalwith the axis of the stem 33.

The operator starts the drill press, thereby causingthe stem 33 torotate with the chuck II, and the operator meanwhile holds theinstrument housing 30 against rotation and at the same time observes thefield of vision through the instrument eyepiece. The line of sightrepresented by the small square II on the field of vision actuallydescribes a circular orbit on the surface of the work piece, but sincethe field of vision constitutes a reference frame for observing relativemovement between the field of vision and the work piece, the orbitalmovement of the field appears to the observer as orbital movement of theintersecting lines I33. In other words, the intersecting dotted linesI03 appear to move in a manner to clearly define a circle I04 in Fig. 4representing the run-out involved, regardless of the origin of therun-out, and the operation axis is at the center of the circle I04. Toplace the work piece accurately for drilling a hole concentric to thereference mark on the work piece, it is merely necessary to shift thework piece until the circular orbit is concentric to the small square 41of the optical system, as indicated in Fig. 4. The operator may thensubstitute a drill for the optical gage with complete assurance that theresultant bore will be accurately located.

The described optical system may provide a magnification of more or lessthan 40 magnitudes, and preferably the cross-hairs employed on thereticle 83 to form the image lines 38 and 40 are spaced apartapproximately .002, the spacing being magnified by the optical system.One of the problems in a precision optical instrument of the presenttype is to avoid apparent shifting of images in the optical fieldincidental to slight changes in position of the observers eye relativeto the optical axis at the eyepiece of the instrument. Any such shift inthe optical field causes corresponding inaccuracy in the centeringprocedure. One method of avoiding such image travel is to employ a verysmall stop aperture to limit the field of vision, but the operator maybe forced to do considerable hunting to bring the reference mark on thework piece into the field of vision if the diameter of the field ofvision is unduly restricted. An advantage of the described opticalsystem is that it inherently minimizes such image travel and thereforepermits using a field of ample diameter.

One feature of the invention is that it may be embodied in an opticalgage, such as shown at I in Fig. 9, with a relativeiy long tubularobjective I35 for centering the work piece with respect to referencemarks at locations difficult of access. In Fig. 9 the desired center isclose to a perpendicular face I91 of a work piece I88.

In some practices of the invention the gage is employed on machinesknown to be so accurately built as to have no inherent run-out. In suchpractices I may use a gage of the above construction with a non-rotarystem, the gage being employed with the machine idle instead of runnmg.

Figs. 5 to 7 show the construction of an optical gage, generallydesignated H3, that I term a variable center scope. The instrument is inlarge part identical in construction with the previously describedinstrument of Figs. 1 to 3, corresponding numerals being employed todesignate corresponding parts. The chief differences to be found in Fig.5 are the substitution of a rigid nonrotating stem or shank III for thepreviously described stem 33 and the employment of a mirror body H2 thatis normally subject to manual adjustment instead of being rigidly fixedafter final assembly.

The stem II 5 is driven with a forced fit into a tubular body I I3 thatis telescoped into the housing body 3 I. The lower portion i iii of thetubular body IE3 corresponds in configuration and function to the block5'! of Fig. 1. As indicated in Fig. 6, this lower portion H5 is cut awayto provide a diametrical face i It that is abutted by the previouslymentioned pair of spaced set screws GI. The two set screws 6i determinethe rotary position of the tubular body H3 about the axis of the housingbody SI, being adjusted to permanent positions when the instrument isassembled at the factory. A set screw IE9 at the outer end of thetubular body H3 may be provided as a precaution to prevent rotation ofthe tubular body after assembly.

The mirror body I I2 is of angular configuration with a polished mirrorface II? and is formed with a pair of ears I I8 that correspond to thepreviously mentioned cars 65. The ears I I8 are pivotally engaged by thepreviously mentioned pointed set screws 6'! to permit the mirror torotate about a transverse axis.

It is contemplated that manually operable" means will be provided tovary the tilt of the mirror face II'I, thereby to vary the direction ofthe first leg 36 of the line of sight provided by the optical system. Inother words, instead of arranging for the leg 36 of the line of sight tobe constantly coaxial with the housing body 3!, it is intended that thisportion of the line of sight be movable to various angles of divergencefrom the axis of the housing body 3|. In the particular constructionshown, the mirror body I I2 may be continuously urged in a rotarydirection against a trimming screw I23 having a knurled head I2I on theexterior of the instrument. Two small springs may be employed for thispurpose, one spring I22 being seated in a bore I23 in the tubular bodyH3, and a second spring I25 being seated in a second and lower bore I26.

It will be noted that the trimming screw I20 corresponds to the upperset screw 0 in Fig. 1 but, unlike the set screw I0, is threaded into thewall of the housing body 3i instead of being threaded into the tubularbody I I3 on which the mirror is mounted. The second arrangement,however, is practical and makes it unnecessary to provide for lateralmovement of the trimming screw when the mirror body i I2 is adjustedabout the vertical axis in the course of factory assembly.

The instrument may be provided with a name plate I2? to cover bores inthe housing body (H, the plate being retained by headed pins I28 thatare driven into bushings I3fl, the bushings being threaded into the twobores 62 shown in Fig. 6 and into a lower bore I3l that is required forinstallation of the lower spring I25.

In this form of the invention the same optical system as previouslydescribed is employed, except that the reticle 83a is' provided withonly a single pair of cross-hairs to extend across the field of vision,as indicated by the two parallel image lines I32 in Fig. 10. It isimportant to note that the cross-hairs are parallel to the transverseaxis about which the mirror body II2 tilts, whereby any change in theangle of tilt of the mirror body about the transverse axis causes theline of sight 36 as well as the whole field of vision to shift in adirection perpendicular to the two image lines I32. A reference mark onthe surface of a work piece to be observed in conjunction with the twocross-hairs consists as before of two lines perpendicular to each otherintersecting at the desired work center. Fig. 10 shows a dotted line I33and an intersecting dotted line I34 constituting such a reference markon the surface of a work piece. The intersection of the two lines I33and I36 may be termed the reference center on the work piece.

The optical gage I If? of Fig. 5 may be mounted in a drill press in thesame manner as indicated in Fig. 8 to locate a reference mark on a Workpiece precisely on the operation axis of the drill press, regardless ofany runout that may be inherent in the drill press and regardless of thecause of such run-out. The initial step in the centering procedure is toorient the pair of parallel image lines I32 either with line I33 or lineI3 of the reference mark and then to maneuver that dotted line into acentral position symmetrical with the two parallel lines. To accomplishthis end, the work piece is moved to bring the reference mark into thefield of vision. Precise orientation and centralization may involveslight axial rotation of the gage and perhaps slight adjustment of thetrimming screw I20. Fig. 10 shows the two image lines I32 strad-p 9dling the reference line I34 at the end of this step.

The reference line I33 may be regarded as representing a first dimensionacross the work piece, the reference line I34 representing a seconddimension across the work piece rotated from the first dimension by lessthan 180. In the present procedure correction for run-out is first madewith reference to line I34, but the direction of relative movement isalong the first dimension or line I33. Thereafter correction is madealong the second dimension.

The second step in the centering procedure with the variable form of theoptical gage is to rotate the gage 180, and nearly always such rotationcauses the line I 34 to take a position in the field of vision spacedfrom the two lines I32, as shown in Fig. 11.

The operator then performs the third step, which consists ofmanipulating the trimming screw I20 to cause the two image lines I32 toshift toward the line I34 until the apparent distance in Fig. 11 betweenthe center of the field and the line I34 is divided by half. The wholefield of vision, of course, shifts with lateral movement of the linesI32 so that the reference mark rather than the optical lines I32 appearsto the operator as making the relative movement, and the field of visionat the end of this step has the appearance indicated by Fig. 12.

In the step just described the line of sight is shifted relative to thereference mark on the work piece, the work piece being stationary. Inthe step that is next performed the line of sight remains stationary,and the operator shifts the work piece until the line I34 is againsymmetrically straddled by the two lines I32, as indicated in Fig. 10.It is apparent that the spacing shown in Fig. 11 between the line I34and the center of the field of vision is taken up by movement of theline of sight relative to the work piece and to an equal extent bymovement of the work piece relative to the line of sight. At this pointthe operator may check the accuracy with which the last two steps havebeen performed by rotating the optical gage 130, the test being thatsuch rotation does not disturb the symmetrical arrangement shown in Fig.10.

The operator may then take the next step of the centering procedure,which step consists of rotating the optical gage 90 to place the twolines 132 parallel with the line I33 of the reference mark, the field ofvision then having the appearance indicated in Fig. 13. Adjustment up tothis point has been along or in the direction of the dimensionrepresented by the line I33, whereas the intention now is to providecorrection along or in the direction of the dimension represented by theline I34. To make this final correction the operator shifts the workpiece in a direction perpendicular to the instant direction of theoptical lines I32 to change the field of vision from the appearance ofFig. 13 to the appearance of 'Fig. 14, thereby placing the intersectionof the two lines I33 and I34 at precisely the center of the field ofvision. 'The reference mark on the work piece is now precisely on theoperation axis of the machine.

The geometrical principles involved in the above described steps of thecentering procedure :may be understood by referring to Figs. 15 to 23.

Fig. 15 shows diagrammatically a mirror body H2 and the'line of sighthaving the two legs 36 and 3 The surface of a work piece is at I35, anda small triangle I3I represents a reference center or center of areference mark on the work piece, while the small circle I38 representsthe unknown location of the operation axis. Fig. 16 shows in plan therelationships that are shown in side elevation in Fig. 15. It will benoted that the discrepancy between the reference center I37 and theoperation axis I38 amounts to the distance a. Of course, the orientationof the reference center I31 with respect to the operation axis I38 andthe magnitude of the discrepancy or run-out are unknown.

In the centering procedure it is not necessary to measure the distance aor to ascertain the orientation of the reference center, since theprocedure automatically deals successively with two components of therun-out, thereby locating the operation axis by successivelycompensating for the two components. Fig. 16 shows a component b and acomponent 0, and it will be readily recognized that the relativemagnitudes of these components for a, given magnitude of run-out willvary with the orientation of the reference center I31.

Fig. 15 shows the line of sight 36 aligned with the reference center I31and corresponds to Fig. 10 showing the field of vision at the end of thefirst step of the centering procedure.

When the instrument is rotated 180, the line of sight 36 is swung to theposition shown in solid lines in Fig. 17, the field of vision then beingas shown in Fig. 11.. As indicated in Fig. 18, this step in a centeringprocedure involves no change in the spatial relationship between thereference center I3! and the operation axis I38. When the trimming screwis manipulated to divide the spacing between the reference center and.the operation axis, the line of sight 3B is shifted to the dotted lineposition of Fig. 17, the shifting being accomplished by tilting of themirror body II2. This point in the procedure is represented by Fig. 12.

In the next step the operator shifts the work piece to change the fieldof vision from the appearance shown in Fig. 12 to the appearance shownin Fig. 10, thereby causing shift of the reference mark I31 relative tothe operation axis I38 to eliminate the component b. Fig. 19 shows theposition of the line of sight 36 at this time, and Fig. 20 shows thecorresponding spatial relationship of the reference center I3! -.to theoperation axis I38.

In continuing the centering procedure, the operator now rotates theinstrument as indicated by the fact that Fig. 21 is rotated on thedrawing 90 from Fig. 19 about the operation axis I38 in Fig. 20. Thediagram shows how the 90 rotation creates the spacing between thereference center I 37 and the line of sight I38 that appears in thefield of vision shown in Fig. 13. When the operator makes the final stepof eliminating this distance by shifting the work piece, the referencecenter is moved into accurate coincidence with the operation axis, asmay be understood by comparing Figs. 20 and 21 with Figs. 22 and 23.Obviously, the lines of the reference mark may intersect at other thanan angle of 90, and likewise the correction for run-out may be alongnon-perpendicular dimensions.

In the centering procedure just described with reference to the drillpress shown in Fig. 8, the work piece is stationary, while the toolholder is adapted. for rotation. The optical gage Ill] may be employedequally well to center work in a machine in which the tool holder isnormally many uses as a sighting device.

stationary and the machine work is accomplished by rotating the workholder. Fig. 24., for example, shows an optical gage H of the presenttype mounted on the tailstock M0 of a lathe for the purpose ofdetermining the correct location of a work piece I l! on the face plateI42 of the lathe. The centering procedure described above with referenceto Figs. to 14 and Figs. 15 to 23 is carried out to position the workpiece M! on the face plate I42, but relative rotation between the gageand the work piece first of 180 and later of 90 is accomplished byrotating the work piece only, the gage being stationary in the tailstockthroughout the procedure.

Figs. 25 and 26 show an embodiment of the described gage in which aspecial gage housing M5 is provided with a unitary base 146 and anonrotatable stem M1, the gage being in all other respects similar tothe gage shown in Fig. l. Preferably the base I46 has a marginal bottomor supporting face M8, the under side of the base being recessed asindicated by the dotted line I49. When the housing 145 is boredlongitudinally in the course of manufacture, three faces are machined onthe sides of the housing equidistant from the longitudinal axis of thehousing. Two of these faces [5!) and i5! are diametrically opposite eachother to lie at the sides of the finished instrument, while the thirdface 52 provides the under surface to rest upon the base 146. Thethickness of the base I46 may be such as to place the longitudinal axisof the housing I exactly one inch or some other dis tance from thesupporting face MB of the base. The required thickness of the base toprovide this spacing may be readily ascertained by carefully measuringthe distance between the two side faces l5i and E51, since half of thatdistance is the distance from the under face 32 of the housing to theaxis of the housing. After the housing is properly mounted on a base,the optical system is accurately corrected by placing the instrument ina suitable jig and observing an accurately located target for guidancein final adjustment of the mirror body in the housing. In the completedinstrument the optical axis or line of sight through the objective ofthe optical system will coincide with the longitudinal axis of thehousing Hi5 and will be exactly parallel to and exactly one inch or someother distance from the lower surface of the base M6.

The instrument shown in Figs. 25 and 26 has Fig. 25, for example, showsthe instrument resting on a gage block H53 to place the optical axis ofthe instrument a desired distance above a reference surface 155, thereference surface being accurately machined. If a work piece I58 isplaced on the reference surface I in focus with the instrument, as shownin Fig. 25, the line of sight provided by the optical system of theinstrument will visually indicate a point on the surface of the workpiece 55 spaced above the reference surface by the same distance as thelongitudinal axis of the instrument.

An important advantage of an optical gage of the type described hereinis that measurements may be made relative to references other thanactual reference marks on a work piece. Thus, the gage may be sightedfor measuring or centering purposes on the edge of a work piece or on acontour of a work piece. The instrument may also be sighted on the edgeor point of a cutting tool for centering or for measuring distances fromthe cutting tool in setting up work.

For example, the spacing between two cutters of a straddle mill may bedetermined by placing the instrument of Fig. 25 in a vise on the worktable of the mill, sighting the instrument on the edge of one rotarycutter, shifting the work table a predetermined distance, and thensighting through the instrument for guidance in the positioning of asecond cutting tool. Any of the described optical gages may be employedfor such purposes as inspecting parts. For ex ample, one of my gages maybe rigidly sighted on a master piece in a jig, the master piece beingthen replaced by work pieces for optical checking.

Various forms of my invention described in specific detail herein forthe purpose of disclosure and to illustrate the principles involved willsuggest to those skilled in the art various changes and substitutionsunder my concept, and I reserve the right to all such departures fromthe disclosure that properly lie within the scope of my appended claims.

I claim as my invention:

1. In an optical gage, the combination of: a housing having acylindrical main bore disposed axially therein, and having an eyepiecemember extending laterally therefrom, said eyepiece memher having anaxial eyepiece bore therethrough intersecting said main bore; a lenssystem in said housing, including a first lens element at one end ofsaid main bore, and a second lens element at the outer end of saideyepiece bore; a cylindrical supporting member in said main bore andaxially aligned therewith and rotatable therein, said supporting memberbeing positioned at the intersection of said bores and having a cutawayportion to provide a light path between said first and second lenselements; means for rotating said supporting member on the main axis ofsaid main bore relative to said housing; a mirror pivotally supported insaid cut-away portion of said supporting member so as to lie in saidlight path and rotatable on a mirror axis perpendicular to said mainaxis; and means for so rotating said mirror to a position in which itdirects light from said first lens element to said second lens elementalong said light path.

2. In an optical gage, the combination of: a housing having acylindrical main bore disposed axially therein, and having an eyepiecemember extending laterally therefrom, said eyepiece member having anaxial eyepiece bore therethrough intersecting said main bore; a lenssystem in said housing, including a first lens element at one end ofsaid main bore, and a second lens element at the outer end of saideyepiece bore; a cylindrical supporting member in said main bore andaxially aligned therewith and rotatable therein, said supporting memberbeing positioned at the intersection of said bores and having a cut-awayportion to provide a light path between said first and second lenselements; means for rotating said supporting member on the main axis ofsaid main bore relative to said housing; a mirror pivotally supported insaid cut-away portion of said supporting member so as to lie in saidlight path and rotatable on a mirror axis perpendicular to said mainaxis; means for s0 rotating said mirror to a position in which itdirects light from said first lens element to said second lens elementalong said light path; and a supporting shank fixed against axialmovement in said main bore in substantially axial alignment with saidfirst lens element and projecting out of said housing.

I I V l 3. A centering gage for mounting on a machine havin a partturnable about an axis of rotation, said gage comprising: a body; meansfor attaching said body to said machine in approximate alignment withsaid axis; optical means carried by said body and providing a field ofvision for establishing a line of sight having a first leg approximatelyaxially aligned with the said axis of rotation and a second leg at anangle thereto, said optical means including a light-deflecting elementat the juncture of said two legs; means supporting said light-deflectingelement for rotation on said body about an axis transverse to the planeof said two legs; and means providing at least one reference line acrosssaid field of vision to indicate the location thereon of said line ofsight, said reference line being substantially parallel with saidtransverse axis whereby rotation of said light-deflecting element causesapparent travel of the reference line in a direction substantiallyperpendicular to the reference line to compensate for run-out in acentering operation.

4. A centering gage of the character described, comprising: a housinghaving a longitudinal light opening and a lateral light opening;lightdeflecting means mounted in said housing to divert light passingthrough said longitudinal opening towards said lateral opening forobservation, whereby the field of vision through said longitudinalopening may be observed from one side of the housing; means supportingsaid light-deflecting means for rotation about a first axis transverseto said longitudinal light opening and further means supporting saidsupporting means in said housing for rotation about a second axisextending axially of the said longitudinal light opening.

5. In an optical gage, the combination of a housing having alongitudinal light opening and a lateral light opening; light-deflectingmeans carried by said housing to divert light passing through saidlongitudinal opening toward said lateral opening for observation wherebythe field of vision through said longitudinal opening may be observedfrom one side of said housing; indicating means in said housingproviding a reference line in said field of vision; a supporting shank,and axially fixed'means mounting said supporting shank on said housingfor free rotation about the longitudinal axis of said housing Whilemaintaining the axial positions of said shank and said housing constantduring rotation, whereby said shank may support said housing forrotation about its longitudinal axis during operation of said gage.

6. A centering gage for mounting on a machine having a componentrevolvable about an axis of rotation, said gage comprising: a body;means for mounting said body on the machine in approximate alignmentwith said axis of rotation; optical means carried by said body forestablishing a line of sight having a first leg approximately axiallyaligned with said axis of rotation and a second leg at an angle thereto,said optical means including a light deflecting element at the junctionof said two legs; and means connecting said light deflecting element tosaid body for rot-ation about an axis normal to the plane of said twolegs whereby to vary the angle between said legs.

7. A gage as set forth in claim 6 wherein said optical means includesindicating means defining a reference line normal-to the plane of saidtwo legs.

8. A centering-gage for mounting on a first holding means of a machinefor use in positioning a work piece relative to a second holding meansof the machine, one of the holding means being revolvable about an axisof rotation passing through the other holding means, the combination of:a body; means carried by said body and connectible to the first holdingmeans of the machine for mounting said body on the first holding meansin approximate alignment with said axis of rotation; optical meanscarried by said body for establishing a line of sight having a first legapproximately coinciding with said axis of rotaton and having a secondleg at an angle thereto, said optical means including a light deflectingelement which is located at the junction of the two legs of said line ofsight and which is rotatable relative to said body about an axis normalto the plane of the two legs, whereby to vary the angle between saidlegs; and adjusting means carried by said body for rotating said lightdeflecting element.

RICHARD STANLEY GRIFFIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,233,176 Brewster July 10, 19171,267,844 Brewster May 28, 1918 1,371,964 Yaggi Mar. 15, 1921 1,520,245Humbrecht Dec. 23, 1924 1,868,908 Lindley July 26, 1932 2,146,906 MollerFeb. 14, 1939 2,184,615 Gunther Dec. 26, 1939 2,202,222 Moller May 28,1940 FOREIGN PATENTS Number Country Date 26,791 Great Britain of 1911173,512 Great Britain Aug. 17, 1922 410,050 Great Britain May 10, 1934

